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Accelerated TOPCon technology advancement changes demand for EVA and POE resin. Topcon pv module

Accelerated TOPCon technology advancement changes demand for EVA and POE resin. Topcon pv module

    Topcon pv module

    In addition to the different technologies of silicon solar cells in crystalline form, TOPCon solar cells have an exceptionally great efficiency of 26%, accomplished by the manufacturing scale technique for industrialization, and have inordinate cell values of 732.3 mV open-circuit voltage (Voc) and a fill factor (FF) of 84.3%. A silicon layer doped with phosphorus and a very thin tunnel oxide form TOPCon. The thickness of tunnel oxide, which is less than 2 nm in the TOPCon cell, primarily affects the electrical properties and efficiency of the cell.

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    TOPCon Solar Cells Fabrication

    The manufacture and construction layout of the cell is fabricated on the front side with a boron emitter and backside with a passivating connecting layer, as well as with equal side fingers applied through a screen-printed approach to build a bi-facial solar cell. Small quantities of oxygen are needed for doping the wafers by phosphorus, including a resistivity value of about 0.4 Ω cm to 1.1 Ω cm. By utilizing a potassium hydroxide (KOH) solution, the wafers are textured on both sides with the pyramids of the irregular pattern. Following the RCA cleaning process and applying the boron tribromide (BBr3) gas, the boron emitter is produced in the furnace of boron diffusion. The backside boron diffusion is removed by applying the etching process on one side by utilizing the solution of nitric acid and hydrofluoric acid (HF/HNO3). The thermal oxidation is performed before the Boron Silicate Glass (BSG) removal. A tunneling SiOx layer is thermally established when wafers are cleaned with chemicals. For the PECVD, silane (SiH4), hydrogen (H2), and phosphine (PH3) are used as precursor gas sources for phosphorus-doped amorphous silicon (n-a-Si:H) growth. After annealing at 900 °C in a N2 environment for the dwell time of 30 min, n-a-Si:H is transformed into phosphorus-doped poly-Si layers (n poly-Si), which comprised n poly-Si on the c-Si/SiOx structure (n poly-Si/SiOx/c-Si contact). The boron emitter that passivated through the layer of the dielectric film, consequently, further RCA cleaning is carried out, specifically similar work out as anti-reflection layer of coating. The backside SiOx/n polysilicon coating is enclosed with PECVD SiNx:H. On both surfaces, an “H-metal contact” with Ag busbars is applied through screen printing for metallization. Subsequently, a quick-firing method with a maximum temperature of approximately 760 °C is applied [1]. Following the fabrication of the TOPCon solar cell, further essential solar cell characterizations such as IV curves and further considerations remain premeditated with a relevant 1-sun (1000 W/m 2 ) IV analyzer.

    Background of TOPCon Solar Cell Development Progress

    In the past few years, the c-Si solar cell has been meticulously studied. When the metal is completely contiguous with the silicon wafer, the consequence is extreme electrical loss owing to the presence of electrons recombination in the solar cell because of the higher absorption of electrons at the junction area. In the preceding model, around two methods remained to decrease the metal carrier recombination accurately within the interaction with the silicon wafer: (1) through retaining a minor layer of the passivated silicon film, and (2) by diminishing the interaction capability and with the help of effortlessly developed doping to separate the metal from silicon wafer [2] [3] [4].

    The main advantage of the foregoing methodologies is a passivated emitter and rear cell (PERC), that is after a conventional PN junction construction, with indigenous doping only in the contact area of the emitter. Currently, its efficiency at the current condition can achieve maximum of 25.0% [5]. The next approach for the previous method is heterojunction with intrinsic thin-layer (HIT) solar cells, as described by the Panasonic company. Such solar cells currently depict an efficiency of these cells around 26.7% [5] [6].

    The TOPCon solar cell can moreover seem as consequential after the typical PN junction structure, associated with the improvements of the two techniques described before. During the past few decades, owing to commendable passivation, the TOPCon solar cell turned out to build for the majority of research across technical organizations. The solar cell having n-type wafer with complete specific selective back contact charge carrier and double-sided interconnected solar cell, including a maximum efficiency, was reported to have approximately 26.7% efficiency by Fraunhofer [5] [6]. The maximum efficiency is owing to the fact wherein the n-type wafer provides a superior impurity that permitted improvement, and the flaws in the faces are passivated entirely. The majority of the materials being revealed that substrate resistivity between 1 and 10 Ω cm utilized for the TOPCon solar cell are able to achieve an efficiency higher than 25% [4]. For the improvement in the efficiency of solar cells and to retain a process that should be capable of continue to enhance, the selective contact charge carrier comes to developed in the proposed TOPCon solar cell. Unlike conventional silicon type of solar cells, TOPCon achieves the following important characteristics and key features [7] [8] :

    The ultimate oxides layer at the nano-scale assured the hanging bond that is found at a single crystal surface, consequently improving the conversion efficiency;

    Depending on the range of substrate conductivity, the oxide layer at nano-scale level permits instant transport of the holes or electrons;

    Owing to the importance of the high possibility of densely doped polysilicon conductivity, the junction resistivity can be reduced, and the output current might become better.

    Structure of TOPCon Solar Cell

    The elementary design of the TOPCon solar cell structure is shown in Figure 1, mainly generated with a PN junction on the substrate of an n-type material [4] [9]. The cell is passivated with a nano-scale layer of aluminum oxide (Al2O3) on the p-type material surface and includes an extremely thin coating of approximately 2 nm with a Silicon dioxide (SiO2) tunneling layer and a highly doped polysilicon layer on the n-type material surface [10]. The surface passivation by the tunneling oxide layer is the most important attribute of the TOPCon solar cell, along with the selective contact to accomplish the exceptionally minimum recombination level after the highly doped layer of polysilicon. To permit many of the carriers to the tunnel, the tunneling layer of SiO2 requires to be sufficiently fine to transport though. Similarly, their field effect must be able to prevent transmission of the minority carriers [11]. Properties of the passivation layer for the highly doped level of the polysilicon layer are varied by adjusting the concentration rate of hydrogen through physical vapor deposition (PVD). For instance, atomic layer deposition (ALD) sputtering, or chemical vapor deposition (CVD) such as plasma-enhanced chemical vapor deposition (PECVD), or low-pressure chemical vapor deposition (LPCVD). Because of the enormous amount of hydrogen atoms in the highly doped polysilicon layer, it shows reasonable properties of passivation [12].

    Figure 1. Schematic representation of the tunneling oxide passivated contact (TOPCon) solar cell layout and elemental fabrication.

    Carrier Transportation Mechanisms at the Poly-Si/SiOx/c-Si Interfaces in the TOPCon Structure

    The trends of pinhole and tunneling are two unique forms of charge carrier transportation configurations that arise at interfaces of poly-Si/SiOx/c-Si. Figure 2 demonstrates the situation of carrier transport that happens at the layer of SiOx. Such structures take place according to the width of SiOx thickness and annealing temperatures.

    Figure 2. Carrier transportation appearance and formal illustration of tunneling and pinholes phenomenon of the tunnel oxide layer in TOPCon solar cell.

    Feldmann et al. explored SiOx tunneling layer experiences maintaining thicknesses of not more than 1.5 nm [13]. The main charge carrier conduction was investigated through the tunneling layer by SiOx. Recent research was enhanced by the simulation modeling performed by Steinkemper et al.

    Likewise, the process of the pinhole occurs with a thickness of more than 2 nm of SiOx that is significantly annealed at higher temperatures of approximately 1000 to 1050 °C. The resulting prevalent technique for such kinds of contacts remained precisely controlled over pinholes within the c-Si layer along with poly-Si which were developed through annealing at a high temperature in the SiOx layer [14] [15]. Although the oxide layer thickness is conflicting in different progress methods [16]. the trend of tunneling takes place in oxides from not more than 2 nm because it is incredibly challenging to tunnel the charge carriers by concentrated oxide coatings [17]. The findings after the performance simulation by Zhang et al. upon nano-scaled tunnel oxide (SiOx, less than 1.5 nm) layer show very high features of tunneling and efficiency by preventing the carrier transport by pinhole [18]. However, a relatively dense SiOx layer (more than 1.1 nm) exhibited minimum fill factor (FF), and efficiency through larger resistivity does not permit any carrier transportation beyond the pinholes.

    The transportation of the minimum carrier over the pinholes improves the FF and minimizes the resistance, consequently enhancing the PCE. Wietler et al. analyzed restrain carrier transport by pinholes through selective etching surface of oxide layer on the junction of the Polo structure [19]. A greater density of pinhole concentration would generate maximum saturation current density and negligible contact resistivity (ρc) of approximately 10 mΩ cm 2. The thickness of the SiOx layer entails the electrical characteristics of the TOPCon solar cell. The current investigation by Wang et al. described three distinct oxide layer thicknesses as 1.25, 1.42, and 1.55 nm, which exhibited inconsistency in efficiency and other electrical parameters of TOPCon solar cells [20]. At 1.55 nm oxide layer thickness, good quality and regular surface are obtained after the etching, and it holds a minimum J0 value of approximately 18 fA/cm 2. with FF = 81.09% and Voc = 687 mV. However, the nano-scaled oxide layer at the thickness of 1.25 and 1.42 nm shows insufficiencies that are ascribed to the passivation failure at the nano-scaled oxide layer along with the pinhole’s progression. Adjusting the accurate temperature for annealing, this one decreases the development of pinhole concentration [21]. The exceptional productivity preceding technology of the TOPCon solar cell continues to determine the specific thickness of the nano-scaled tunnel oxide layer and efficient pinhole concentration for the enhancement in efficiency. The TOPCon solar cell structure holds the lowest value of saturation current density (J0) for equally p-type and n-type poly-Si around (J0 = 2 to 8 fA/cm 2 ). Previously, the doping of poly-Si through phosphorous had better qualities than the poly-Si with boron-doping [22]. However, through research, it became obvious that the n-TOPCon has a good property for the layer of passivation between c-Si wafers of p-type and n-type, demonstrating an excellent value of Voc in comparison with the p-TOPCon [23].

    It is not only tunneling that moves the charge through the pinholes; both the transportation through the pinholes and the tunneling occurs together. For example, excessively thick oxide might provide a high tunneling barrier, although charge transfer through pinholes is possible. However, tunneling is more prevalent in the case of dense nano-scaled oxide. The type of conductivity is the factor that matters most. Due to the Band-bending orientation, it was shown that p-Si/SiOx/p-Si can only transport holes and not electrons, and vice versa.


    • Chen, D.; Chen, Y.; Wang, Z.; Gong, J.; Liu, C.; Zou, Y.; He, Y.; Wang, Y.; Yuan, L.; Lin, W.; et al. 24.58% total area efficiency of screen-printed, large area industrial silicon solar cells with the tunnel oxide passivated contacts (i-TOPCon) design. Sol. Energy Mater. Sol. Cells 2019, 206, 110258.
    • Fırat, M.; Radhakrishnan, H.S.; Payo, M.R.; Choulat, P.; Badran, H.; van der Heide, A.; Govaerts, J.; Duerinckx, F.; Tous, L.; Hajjiah, A.; et al. Large-area bifacial n-TOPCon solar cells with in situ phosphorus-doped LPCVD poly-Si passivating contacts. Sol. Energy Mater. Sol. Cells 2022, 236, 111544.
    • Yan, D.; Cuevas, A.; Bullock, J.; Wan, Y.; Samundsett, C. Phosphorus-diffused polysilicon contacts for solar cells. Sol. Energy Mater. Sol. Cells 2015, 142, 75–82.
    • Rohatgi, A.; Zimbardi, F.; Rounsaville, B.; Benick, J.; Stradins, P.; Norman, A.; Lee, B.; Upadhyaya, A.; Ok, Y.W.; Tao, Y.; et al. Overcoming the Fundamental Bottlenecks to a New World-Record Silicon Solar Cell; Final Technical Report (No. DOE-GT-6336); Georgia Institute of Technology: Atlanta, GA, USA, 2017.
    • Green, M.A.; Dunlop, E.D.; Hohl-Ebinger, J.; Yoshita, M.; Kopidakis, N.; Bothe, K.; Hinken, D.; Rauer, M.; Hao, X. Solar cell efficiency tables (Version 60). Prog. Photovolt. Res. Appl. 2022, 30, 687–701.
    • Younis, I.M. Cost Benefit Analysis of Photovoltaic Technology Adoption at Rest and Service Area for Malaysia Highway. Ph.D. Thesis, Universiti Teknologi Malaysia, Johor, Malaysia, 2019.
    • Lauinger, T.; Schmidt, J.; Aberle, A.G.; Hezel, R. Record low surface recombination velocities on 1 Ω cm p-silicon using remote plasma silicon nitride passivation. Appl. Phys. Lett. 1996, 68, 1232–1234.
    • Grant, N.E.; Markevich, V.P.; Mullins, J.; Peaker, A.R.; Rougieux, F.; Macdonald, D.; Murphy, J.D. Permanent annihilation of thermally activated defects which limit the lifetime of float-zone silicon. Phys. Status Solidi (A) 2016, 213, 2844–2849.
    • Steinhauser, B.; Feldmann, F.; Polzin, J.I.; Tutsch, L.; Arya, V.; Grübel, B.; Fischer, A.; Moldovan, A.; Benick, J.; Richter, A.; et al. Large area TOPCon Technology Achieving 23.4% Efficiency. In Proceedings of the 2018 IEEE 7th World Conference on Photovoltaic Energy Conversion (WCPEC) (A Joint Conference of 45th IEEE PVSC, 28th PVSEC 34th EU PVSEC), Waikoloa, HI, USA, 10–15 June 2018; pp. 1507–1510.
    • Lindekugel, S.; Lautenschlager, H.; Ruof, T.; Reber, S. Plasma Hydrogen Passivation for Crystalline Silicon Thin-Films. In Proceedings of the 23rd European Photovoltaic Solar Energy Conference, Valencia, Spain, 1–5 September 2008; pp. 2232–2235.
    • Richter, A.; Glunz, S.W.; Werner, F.; Schmidt, J.; Cuevas, A. Improved quantitative description of Auger recombination in crystalline silicon. Phys. Rev. 2012, 86, 165202.
    • Feldmann, F.; Fellmeth, T.; Steinhauser, B.; Nagel, H.; Ourinson, D.; Mack, S.; Lohmüller, E.; Polzin, J.I.; Benick, J.; Richter, A.; et al. Large Area TOPCon Cells Realized by a PECVD Tube Process. In Proceedings of the 36th European Photovoltaic Solar Energy Conference and Exhibition, Lisbon, Portugal, 10 September 2021.
    • Feldmann, F.; Nogay, G.; Loper, P.; Young, D.L.; Lee, B.G.; Stradins, P.; Hermle, M.; Glunz, S.W. Charge carrier transport mechanisms of passivating contacts studied by temperature-dependent JV measurements. Sol. Energy Mater. Sol. Cells 2018, 178, 15–19.
    • Haase, F.; Kiefer, F.; Schafer, S.; Kruse, C.; Krugener, J.; Brendel, R.; Peibst, R. Interdigitated back contact solar cells with polycrystalline silicon on oxide passivating contacts for both polarities. Jpn. J. Appl. Phys. 2017, 56, 08MB15.
    • Folchert, N.; Rienacker, M.; Yeo, A.A.; Min, B.; Peibst, R.; Brendel, R. Temperature-dependent contact resistance of carrier selective Poly-Si on oxide junctions. Sol. Energy Mater. Sol. Cells 2018, 185, 425–430.
    • Richter, A.; Benick, J.; Feldmann, F.; Fell, A.; Steinhauser, B.; Polzin, J.I.; Tucher, N.; Murthy, J.N.; Hermle, M.; Glunz, S.W. September. Both sides contacted silicon solar cells: Options for approaching 26% efficiency. In Proceedings of the 36th European PV Solar Energy Conference and Exhibition, Marseille, France, 9–13 September 2019; pp. 9–13.
    • Peibst, R.; Romer, U.; Larionova, Y.; Rienacker, M.; Merkle, A.; Folchert, N.; Reiter, S.; Turcu, M.; Min, B.; Krugener, J.; et al. Working principle of carrier selective poly-Si/c-Si junctions: Is tunnelling the whole story? Sol. Energy Mater. Sol. Cells 2016, 158, 60–67.
    • Zhang, Z.; Zeng, Y.; Jiang, C.S.; Huang, Y.; Liao, M.; Tong, H.; Al-Jassim, M.; Gao, P.; Shou, C.; Zhou, X.; et al. Carrier transport through the ultrathin silicon-oxide layer in tunnel oxide passivated contact (TOPCon) c-Si solar cells. Sol. Energy Mater. Sol. Cells 2018, 187, 113–122.
    • Wietler, T.F.; Tetzlaff, D.; Krugener, J.; Rienacker, M.; Haase, F.; Larionova, Y.; Brendel, R.; Peibst, R. Pinhole density and contact resistivity of carrier selective junctions with polycrystalline silicon on oxide. Appl. Phys. Lett. 2017, 110, 253902.
    • Wang, Q.; Wu, W.; Yuan, N.; Li, Y.; Zhang, Y.; Ding, J. Influence of SiOx film thickness on electrical performance and efficiency of TOPCon solar cells. Sol. Energy Mater. Sol. Cells 2020, 208, 110423.
    • Zeng, Y.; Tong, H.; Quan, C.; Cai, L.; Yang, Z.; Chen, K.; Yuan, Z.; Wu, C.H.; Yan, B.; Gao, P.; et al. Theoretical exploration towards high-efficiency tunnel oxide passivated carrier-selective contacts (TOPCon) solar cells. Sol. Energy 2017, 155, 654–660.
    • Lenes, M.; Naber, R.C.G.; Luchies, J.R.M. LPCVD Polysilicon Passivated Contacts for Different Solar Cell Concepts. In Proceedings of the 6th Silicon PV Conference, Chambery, France, 7 March 2016.
    • Rehman, A.U.; Lee, S.H. Advancements in n-type base crystalline silicon solar cells and their emergence in the photovoltaic industry. Sci. World J. 2013, 2013, 470347.

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    Accelerated TOPCon technology advancement changes demand for EVA and POE resin

    Amid the pursuit of carbon neutral, the world’s major regions introduced policies that favor renewable energy, driving up renewable energy demand significantly. Solar installation has experienced exponential growth in recent years, beating forecast. Of all the elements, continued technology advancement underpins the solar development. PERC, emerged in 2015, and replaced Back Surface Field (BSF) to become mainstream in 2019, will remain its dominance in the two to three years to come. Yet, it’s inevitable that PERC cells are reaching its theoretically limit, a situation leading to the turning point in the technology.

    Facilitated TOPCon technology development

    Discussion on the next generation technology after PERC revolves around n-type TOPCon and HJT, as well as xBC. The three techniques can co-exist in the market, but how fast it can help improve cell efficiency and costs will determine their position and capacity expansion. Of which, TOPCon is more favorable by traditional cell and module manufacturers due to its compatibility with PERC lines. As of September, announced TOPCon capacity expansions have surpassed 350 GW, with more than 40 GW having been materialized. As Jinko, Tongwei, Trina, and JA Solar scaling up their TOPCon expansion, nameplate capacity is likely to exceed 70 GW by the end of the year.

    Against the backdrop of significant growth in TOPCon capacity and production of leading manufacturers, InfoLink estimates that TOPCon shipment will stand at around 20 GW this year, an evident growth compared with 2 GW to 3 GW in the past. Its market share is likely to reach 7%. In 2023, shipment of which is expected to rise to 60 GW, with market share increasing to 20%. TOPCon is forecast to reach beyond 100 GW of shipment and hit 30% of market share in 2024.

    POE encapsulant dovetails with TOPCon

    Module assembly is one key processing step in the solar supply chain, and the rapidly growing industry spurs demand for encapsulant. EVA, with better optical performance, binding property, and lower costs, as well as good compatibility with p-type cells and modules, has dominated the market over the past decade. POE, with better moisture barrier as well as higher weather resistance and PID resistance, becomes a better option for n-type manufacturers as TOPCon emerges. This is because TOPCon cells, whose front silver contains aluminum, are more sensitive to water vapor, and thus requires stronger water barrier. EVA, on the other hand, may decompose and produce acid in hot and humid environment, thereby reacting with the glass and corrode the busbar, resulting in module performance degradation. Therefore, major n-type module manufacturers have either explored or adopted pure POE encapsulant or encapsulant that contains POE resin.

    Resin resin supply and demand

    As global solar installation rose to nearly 270 GW this year, module production is estimated to come in at 340 GW considering sea shipping and inventory factors. This translates to around 1,520,000 MT of resin demand. Of which, 1,270,000 MT comes from EVA resin and 250,000 MT from POE resin. Comparing with 1,330,000 MT of EVA and 310,000 MT of POE resin supply this year, supply is tight against demand.

    Looking ahead, global neutral demand for modules is projected to hit 326 GW in 2023 and 380 GW in 2024, with total module production estimating to surpass 400 GW in 2023 and reach nearly 500 GW in 2024, if factoring inventory. over, as TOPCon capacity continues to grow, demand for POE resin will also grow rapidly. Demand will differ depending on the encapsulation encapsulant used by TOPCon manufacturers, as shown by following scenarios:

    Scenario 1: If TOPCon modules use EPE encapsulant for both sides on glass-glass or glass-backsheet module, such combination will have the lowest demand for POE resin. Under this scenario, demand for EVA and POE resin will respectively sit at 1,670,000 MT and 300,000 MT in 2023 and 1,780,000 MT and 360,000 MT in 2024. Given an estimated EVA resin supply of 1,690,000 MT in 2023, supply will run short in this case.

    Scenario 2: If TOPCon glass-backsheet modules use pure POE encapsulant on the front and EVA encapsulant on the rear side, while 70% of glass-glass modules use pure POE encapsulant on both sides and 30% of glass-glass modules use EPE encapsulant on both sides, demand for EVA and POE resin will respectively come in at 1,530,000 MT and 390,000 MT in 2023 and 1,530,000 MT and 520,000 MT in 2024. Under this scenario, 2023 will see tight EVA resin supply, while 2024 will see tight POE resin supply.

    Scenario 3: If TOPCon glass-backsheet modules use pure POE encapsulant on the front and EVA encapsulant on the rear side, while glass-glass modules use pure POE encapsulant, demand for EVA and POE resin will respectively come in at 1,480,000 MT and 420,000 MT in 2023 and 1,450,000 MT and 580,000 MT in 2024. Given the estimated POE resin supply in 2023 and 2024 is 475,000 MT and 590,000 MT, respectively, POE resin will be in tight supply in 2023 and become extremely tight in 2024.

    Scenario 4: If TOPCon modules use pure POE encapsulant on both sides for glass-glass and glass-backsheet formats, demand for POE resin will be the highest. Under this scenario, demand for EVA and POE resin will respectively come in at 1,420,000 MT and 480,000 MT in 2023 and 1,350,000 MT and 660,000 MT in 2024. In this case, POE resin supply will run short in 2023 and 2024.

    As per InfoLink’s investigation, scenario 2 and 3 are more similar to the actual situation, which estimates demand for EVA and POE resin respectively come in at 1,480,000-1,530,000 MT and 390,000-420,000 MT in 2023; 1,450,000-1,530,000 MT and 520,000-580,000 MT in 2024. Combing EVA and POE resin, supply of both will be tight in 2023. In 2024, supply of EVA resin will start to see surplus, while POE supply will become short.

    POE proves itself to be a better product for n-type modules with its performance in water vapor barrier and PID resistance. Currently, POE resin is mainly supplied by Dow, LG, and Mitsui Chemicals. The growth of POE resin will rely on these manufacturers’ allocation of production lines to PV customers. Domestic POE production in China will not release until after 2024. If the penetration rate of n-type products improves or POE manufacturers overseas are unable to deliver POE resin to PV manufacturers, POE supply may fall short of demand, while module manufacturers will be forced to use encapsulant that is not consisted of purely POE.

    Evaluating New N-Type PV Modules

    Next-generation n-type PV cells are essential to the solar industry’s continued ability to drive down costs while improving performance.

    In 2022, RETC is closely monitoring a technology trend quickly gaining market traction and acceptance: the rise of next-generation n-type PV cells with passivating contacts. Here, we explore the promise of new n-type PV cell designs—and the potential challenges associated with scaling this promising technology.


    Many industry analysts and material scientists believe emerging n-type PV cell designs are the next logical progression on the PV technology roadmap. In 2013, researchers at Germany’s Fraunhofer Institute for Solar Energy Systems presented a method of producing high-efficiency n-type silicon solar cells with a novel tunnel oxide passivated contact (TOPCon) structure. This novel cell design achieved high marks for open-circuit voltage (Voc), fill factor and efficiency thanks to excellent surface passivation and effective carrier transport.

    Less than a decade later, TOPCon is the buzziest word in solar. The largest module manufacturers in the world are beginning volume production of PV modules with TOPCon cells. While LONGi Solar is betting big on p-type TOPCon, many other leading module companies—such as Jinko Solar, Jollywood Solar Technology, JA Solar and Trina Solar—are making substantial investments in modules with n-type TOPCon cell designs.

    This collective pivot in the market is primarily due to flattening efficiency curves for the p-type passivated emitter and rear-contact cell (PERC) modules. Although these have dominated the market in recent years, manufacturers are starting to reach the physical limits of p-type mono PERC cell designs. Transitioning to n-type TOPCon cells will allow module companies to boost cell efficiencies further in the laboratory and mass production.

    “Everybody wants the highest possible module nameplate rating,” explains Kenneth Sauer, principal engineer at VDE Americas. “Via higher open-circuit voltage values, you can achieve higher efficiencies and power ratings. In and of itself, that will likely move manufacturers to n-type TOPCon cell designs, as soon as they can get there.”


    Solar manufacturers have long recognized the potential efficiency benefits of n-type PV cells. For example, Sanyo began developing n-type heterojunction technology (HJT) PV cells in the 1980s. In addition, SunPower has built its interdigitated back contact (IBC) PV cells upon a base of high-purity n-type silicon.

    Due to the manufacturing complexities involved, high-efficiency PV modules based on n-type HJT and IBC cell designs are relatively expensive to produce and remain a niche part of the market. By comparison, n-type TOPCon cell manufacturing is similar to the PERC process. As a result, manufacturers can produce these next-generation high-efficiency TOPCon modules on upgraded PERC production lines.

    Though today’s n-type TOPCon modules cost slightly more to produce on a per-watt basis than p-type mono PERC modules, the efficiency gains result in a lower levelized cost of energy (LCOE) in large-scale field deployments. Best of all, leading experts expect n-type TOPCon to benefit from an accelerated learning curve.

    A primary material advantage of n-type TOPCon cells relative to p-type mono PERC cells is a lower degradation rate due to a decreased susceptibility to both light-induced degradation (LID) and light- and elevated temperature–induced degradation (LeTID). Additional advantages may include a higher bifaciality factor, as well as improved performance under both low-light and high-temperature conditions.


    Most analysts expect modules with n-type TOPCon cells to quickly increase market share based on these performance advantages. However, emerging PV cell technologies—even ones that ultimately prove successful in the field—invariably carry more risk than mature and proven technologies. Until industry stakeholder have deployed products at scale, the potential exists for as-yet-undiscovered degradation mechanisms.

    Today, for example, independent engineers and financiers consider p-type mono PERC PV modules a stable and low-risk technology. This assessment was not always a consensus opinion. Early versions of mono PERC modules had issues with stability, especially LID and, in rare instances, LeTID. These unexpected mono PERC degradation modes demonstrate the performance risks that early adopters face with new technologies.

    While n-type TOPCon PV cells have proven resilient to LID and LeTID, some evidence exists of susceptibility to ultraviolet-induced degradation (UVID). For example, researchers at the SLAC National Accelerator Laboratory and the National Renewable Energy Laboratory (NREL) have documented front- and back-side power loss in advanced solar cell technologies after artificially accelerated UV exposure testing. These data do not point to a single degradation mechanism but suggest that different cell designs degrade via different pathways.


    Though it is impossible to eliminate all risk and uncertainty associated with technological innovation, artificially accelerated exposure tests—such as those conducted at RETC’s accredited laboratories—are a proven method of identifying novel failure and wearout mechanisms. Beyond-qualification and bankability test sequences and protocols are clearly valuable to manufacturers bringing new products to market. They are also critically important to developers, financiers and independent engineers seeking to de-risk early deployments of next-generation technologies.

    “As someone who provides technical advisory services,” says Sauer at VDE Americas, “I recommend conducting accelerated UVID testing for new n-type modules as part of a technical due diligence survey. If cell passivation layers are not properly tuned, they can break down with UV exposure. Given all of the new cell designs coming to market, it is important to evaluate each one individually on a case-by-case basis.”

    accelerated, topcon, technology, advancement

    Given the high stakes involved, RETC is independently subjecting a variety of next-generation modules with advanced n-type cell designs to highly accelerated UV testing. “We’re not trying to sound an alarm for no reason,” explains CEO Cherif Kedir. “We just want to test the potential for UV degradation to educate ourselves and the industry. If there’s no problem, we can all move forward with our lives. If there is a problem, we will publish a report so that the industry can get out in front of the issue.”

    Topcon pv module

    TOPCon technology has been a buzzword in the solar industry since 2016, but it officially entered mass production only in 2019. We all know that various cell technologies are competing in the market, and manufacturers are constantly looking for new alternative technologies to develop better and more efficient panels because the limits of PERC cells have been reached. TOPCon technology (Tunnel Oxide Passivated Contact) is a cutting-edge cell technology that is causing a stir in the industry.

    Let’s see more details about it in this article.

    What is TOPCon Technology?

    Solar cells are made from silicon wafers. In order to generate voltage from sunlight (hence the name photo-voltaic), the silicon wafer is doped with chemicals. When the silicon wafer is doped with Boron it creates P-type silicon, whereas doping with Phosphorus creates N-type silicon. When the N-type and P-type silicon come in contact, a junction is formed (the P-N junction) which generates an electric field in the material and helps in developing the voltage across the solar cell. A N-type solar cell basically means the silicon wafer was initially N-type (i.e. phosphorus doped) on which some Boron was diffused on the top side to create the P-N junction. Since the bulk silicon is free from Boron, this N-type cells do not degrade in sunlight like the P-type cells (a phenomenon called LID, due to the formation of Boron-Oxygen complexes in P-type solar cells).

    The TOPCon solar cells are generally made from N-type cells by adding some additional layers to the cell. The additional layers (of SiO2 and Phosphorus-doped poly-silicon) are added at the rear side of the solar cell before adding the metallic contacts. Their role is to improve the passivation at the contacts (basically facilitating the transfer of the light-generated electrons from the silicon cell to the metallic contact with minimum losses). This leads to higher open circuit voltage of the solar cells and hence higher cell efficiency.

    TOPCon Solar Cell Operation

    Fig. Cross-sectional view of the TOPCon solar cell

    • Sunlight is incident on the solar cell from the top side (and also from the bottom side in the case of bifacial cells) and gets absorbed in silicon material.
    • Absorption of sunlight generates electron-hole pairs. Actually, the electrons in the valence Band absorb the light energy and jump to a higher energy state (conduction Band) in which it can flow freely from atom to atom (not bound to any one atom). Holes are basically the vacancies left behind in the Valence Band when the electron jumps to the conduction Band. These holes can be considered positive charge carriers (but they move in the valence Band in the opposite direction to electrons).
    • At the junction of the P-type and N-type regions, there is an electric field that causes the photo-generated electrons to flow to the N-type region and the corresponding Holes to the P-type region. This separates the electron from the hole, which would otherwise recombine to give backlight.
    • These photo-generated electrons that cross the P-N junction region, now move to the bottom side of the N-type layer towards the rear contact.
    • Electron-hole pairs are also getting generated in the bulk (N-type layer). If these holes are present near the rear contacts, then they can cause recombination (as Metal – Silicon Contact region acts as a powerful recombination centre), leading to the loss of the photo-generated electrons.
    • Here the concept of Tunnel Oxide Passivated Contact (TOPCON) comes into play. The 1-2 nm thin layer of SiO2 tunnel oxide acts like a selective gate allowing only electrons to pass through it to the rear side (and stopping any holes). Further, the n Poly silicon layer creates an electric field which attracts the electrons (and repels the holes). This ensures that a high number of electrons reaches the bottom side silver contacts where they are collected by the interconnect ribbons and sent to the external load circuit.

    Pros of TOPCon Technology

    It can be manufactured in the same machines as P-type Multi-Busbar modules (like the Mono PERC production lines), which means that the module manufacturers have to bear no additional cost to manufacture TOPCon modules.

    Compared to P-type Mono PERC cells, TOPCon cells are more efficient at converting solar energy into electricity, increasing both cell and module efficiency. The maximal efficiency of TOPCon cells is 28%, while that of PERC cells is only about 24%.

    In comparison to PERC panels, TOPCon modules exhibit a reduced rate of power degradation both in the first year and over the course of the panel’s 30-year operational life.

    The percentage of power production lost by a solar panel with each degree of temperature increase is known as the temperature coefficient. In hot conditions, it affects the power generation of PV modules.

    Since TOPCon cells are less impacted by temperature increases, TOPCon modules’ effectiveness will be higher in hot climates compared to PERC Modules.

    TOPCon cells have a higher Bifaciality factor than PERC modules. It is an important factor as bifacial solar modules are getting more and more popular in the market.

    Since TOPCon modules are more efficient in low light, the daytime power generation period is extended and the annual energy output of the PV system is increased.

    Rayzon adopted Topcon technology because it allows improving the overall performance of the solar panel system which increases its electricity production by absorbing more photons from sun rays in the highest latitudes area of the earth.

    In conclusion, Rayzon Solar is the industry’s future, and we hope this article has given you some useful understanding of TOPCon technology. Rayzon Solar is one of the leading manufacturers in the solar sector adopting cutting-edge TOPCon technology for commitment to sustainability. We urge you to choose solar panels to generate electricity and move from black energy to green energy. Let’s make Our future more vibrant and sustainable.

    TOPCon Solar Cells: Everything You Should Know About It

    PERC (passivated emitter rear contact) technology has been ruling the solar power industry for a long time. While it has a theoretical efficiency of around 24%, PERC technology is still lacking as it leads to recombination loss due to metal contact. For this reason, passivated contact technology has remained at the top of investigations into photovoltaics for several years. Within this technology field, there seems to be a top contender—TOPCon (Tunnel Oxide Passivated Contact) Solar Cells.

    TOPCon is an advanced N-type silicon cell technology that helps mitigate recombination losses and increase cell efficiency. So, it’s no surprise that this technology is creating a buzz in the renewable energy industry.

    Here is a complete guide to help businesses understand the ins and outs of TOPCon solar cells, and how they could revolutionize generating solar power.

    Global market summary of solar cells

    The solar cell market is experiencing massive traction worldwide, and it may reach a Compound Annual Growth Rate or CAGR of 17.72% between 2022 to 2030. In 2021, the solar cell market was about 85 billion; by 2030 it’s expected to exceed 369 billion.

    These numbers are impressive due to the increase in concerns for the rising carbon footprints worldwide throughout different economic sectors. In the next seven years, demand is projected to rise due to an increased need for clean, environmentally friendly, and dependable sources that will drastically reduce reliance on fossil fuels.

    In short, the solar cell market is currently competitive with other fuels because of its cost-effectiveness. Another key driver of this market is the growing investments in renewable energy sources for electricity, and government incentives like tariffs, tax breaks, etc., that encourages investments.

    The technology behind TOPCon solar cells

    Before we try to understand the technology behind TOPCon solar cells, let’s take a brief look at PERC technology–since the general scheme of a PERC and TOPCon solar cell are quite similar.

    PERC solar cells feature an extra dielectric passivation layer at the back of the cell that captures more sun rays, reflecting them into the solar cell for conversion to electricity for increased efficiency. There are two types of PERC solar cells:.type and P-type.

    The primary difference between a p-type and n-type PERC cell is in the atoms their silicon wafer is doped with, which affects their number of electrons. In p-type PERC cells, the silicon layer is doped with boron, meaning there is a deficit of one electron, making the cell positively charged. On the other hand, n-type PERC cells are doped with phosphorus, meaning an extra electron, making it negatively charged. In short, n-type PERC cells are usually more efficient than p-type cells.

    Now, let’s move on to TOPCon solar cells.

    TOPCon solar cells use a micro-nano tunneling oxide layer and an intrinsic, carrier-selective, polysilicon layer at the back. Also, a dielectric stack and an anti-reflection layer passivate the front end. Together, these components offer high-efficiency and cutting-edge passivation contact technology. The thin silicon layer serves as the surface passivation layer, enabling a two-way enhancement in passivation performance and electrical conductivity, which minimizes subsurface recombination.

    TOPCon cells are similar to n-PERC solar cells. Hence, unlike other potential new technologies, existing PERC solar cells can be easily upgraded to TOPCon solar cells by adding a tunnel oxide passivation layer. This upgrade reduces the total cost of improving the efficiency of existing PERC lines and provides updated technological innovations.

    TOPCon solar cells: the greater benefits

    TOPCon is a promising solar cell technology that could replace other technologies in the industry, such as PERC/PERT and HJT, that is quickly inching toward their efficiency limit or come with significant long-term costs. Here are two vital benefits of TOPCon solar cells that could help it become mainstream in the near future.

    High upper limit of efficiency

    TOPCon solar cells prove to be an attractive option as businesses crave alternative solar cell technologies with low manufacturing costs, less-complicated procedures, and higher efficiency potential.

    accelerated, topcon, technology, advancement

    TOPCon solar cells feature N-type silicon, which offers both efficiency and stability, unlike other technologies in the solar power industry with issues like high LID and LeTID degradation.

    Several studies have found the upper limit of theoretical efficiency for TOPCon solar cells to be around 28.2 to 28.7%. This efficiency is far greater than PERC cells, which stand at 24.5%. And a higher efficiency leads to more energy harvesting per unit area.

    Adaptable manufacturing process

    As stated earlier, TOPCon is much like a modified version of PERC cells. So, TOPCon solar cells can be easily manufactured by adding a few extra processes to the well-matured PERC manufacturing processes and product lines. This compatibility between the two technologies means that adopting the TOPCon technology is more accessible to those already using PERC cells.


    TOPCon solar cells offer a combination of unparalleled efficiency, relatively low capital costs, and the capability to fit into existing module design parameters easily. While other n-type solar cell technologies like IBC and HJT exist, they demand unique cell lines and higher capital costs. Hence, TOPCon solar cells are worth considering.

    accelerated, topcon, technology, advancement

    Several solar module companies, including LONGi and TrinaSolar, have already updated their production lines, and more are planning to do so soon. So, the renewable energy industry can expect TOPCon to grow and become as universal as PERC technology.

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